vm-migration: Snapshot should have a unique SnapshotDataSection

There's no reason to carry a HashMap of SnapshotDataSection per
Snapshot. And given we now provide at most one SnapshotDataSection per
Snapshot, there's no need to keep the id part of the SnapshotDataSection
structure.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

virtio-devices/src/transport/pci_device.rs

@@ -522,7 +522,7 @@ impl VirtioPciDevice {
 
         let state: Option<VirtioPciDeviceState> = snapshot
             .as_ref()
-            .map(|s| s.to_versioned_state(&id))
+            .map(|s| s.to_versioned_state())
             .transpose()
             .map_err(|e| {
                 VirtioPciDeviceError::CreateVirtioPciDevice(anyhow!(